NET (National Eligibility Test) is an entrance exam which is organized to select the aspirants for the post of Assistant Professor and for awarding Junior Research Fellowship to the deserving candidates. The NET Exam is conducted by 1.Council of Scientific and Industrial Research (CSIR) only for the aspirants who belongs from science stream. 2. Central Board of Secondary Education (CBSE) for the aspirants like (History, Economics, Management etc) To know more about the NET Exam you can visit here - https://goo.gl/NCM84U I hope it helps!

As you have completed Masters degree you are eligible to appear for NET Exam. CSIR and UGC are two different governmental departments conduct their respective NET entrance exam and that is UGC NET exam OR CSIR NET exam.
For details about NET Exam click here